In the oil and gas industry, it is imperative to know and understand the material properties of compositions used during drilling and exploration and to determine how these properties are affected by temperature, pressure and time. Various tests require that a material, compound or formulation, be subjected to testing at temperatures above ambient temperature.
An exemplary material test utilizes a viscometer to determine the viscosity of a fluid sample wherein a sample is rotated in relation to an immersed sensor element such as a bob. It is often desirable to conduct such measurements at above-ambient temperatures.
To do this, the sample is routinely placed in a sample cup having specified dimensions. During testing the sample is arranged within a heating unit with a bob of specified dimension located in the sample cup. Typically, an oil-based or water-based fluid is retained in the heating unit intermediate the heating unit interior surfaces and the sample vessel exterior surfaces to provide efficient heat transfer from the heating unit to the sample vessel and consequently to the sample.
The heating unit typically has an insulating chamber to limit heat dissipation to the environment.
Conventional heating units for instruments that test fluid properties typically comprise a container constructed to hold a liquid heating medium, typically an oil. Heaters are used to apply heat to the heating unit's retaining wall which is in direct contact with the heating liquid, thus increasing the liquid's temperature. The sample vessel is at least partially surrounded by the liquid inside the heating jacket. The liquid imparts heat to the sample vessel through conduction heating. In this system, the retaining surface of the heating unit is typically machined aluminum and the exterior surface of the sample vessel is a corrosion-resistant alloy.
A second conventional heating apparatus uses a machined graphite block to replace the oil. The graphite block is machined to directly contact the outer surfaces of the sample vessel. Heaters apply heat directly to the graphite block, which increases the block's temperature. An exemplary heating apparatus using graphite block is marketed by Chandler Engineering as Model No. 5550 HPHT Viscometer.